Editing Chloroplast (section)

=== Primary endosymbiosis ===

{{Plain image with caption|Chloroplast endosymbiosis simple.svg|'''Primary endosymbiosis'''<br />A eukaryote with [[Mitochondrion|mitochondria]] engulfed a [[cyanobacterium]] in an event of [[Serial endosymbiosis|serial]] primary endosymbiosis, creating a [[Archæplastida|lineage]] of cells with both organelles.<ref name="Campbell-2009c" />|400px|right|bottom|triangle|#1abc31}}

Approximately two{{Nbsp}}billion years ago,<ref name="Milo" /><ref name="Sánchez-Baracaldo-2017">
{{cite journal | vauthors=Sánchez-Baracaldo P, Raven JA, Pisani D, Knoll AH | title=Early photosynthetic eukaryotes inhabited low-salinity habitats | journal=Proceedings of the National Academy of Sciences of the United States of America | volume=114 | issue=37 | pages=E7737–E7745 | date=September 2017 | pmid=28808007 | pmc=5603991 | doi=10.1073/pnas.1620089114 | bibcode=2017PNAS..114E7737S | doi-access=free }}</ref><ref>{{Cite journal |last1=Falcón |first1=Luisa I |last2=Magallón |first2=Susana |last3=Castillo |first3=Amanda |date=4 March 2010 |title=Dating the cyanobacterial ancestor of the chloroplast |url=https://academic.oup.com/ismej/article/4/6/777/7588052 |journal=The ISME Journal |language=en |volume=4 |issue=6 |pages=777–783 |doi=10.1038/ismej.2010.2 |pmid=20200567 |bibcode=2010ISMEJ...4..777F |issn=1751-7362}}</ref> a free-living [[cyanobacterium]] entered an early [[eukaryotic]] cell, either as food or as an internal [[parasite]],<ref name="Campbell-2009c" /> but managed to escape the [[phagocytic vacuole]] it was contained in and persist inside the cell.<ref name="Kim-2009" /> This event is called ''[[endosymbiosis]]'', or "cell living inside another cell with a mutual benefit for both". The external cell is commonly referred to as the ''host'' while the internal cell is called the ''endosymbiont''.<ref name="Campbell-2009c" /> The engulfed cyanobacteria provided an advantage to the host by providing sugar from photosynthesis.<ref name="Campbell-2009c" /> Over time, the cyanobacterium was assimilated, and many of its genes were lost or transferred to the [[nuclear genome|nucleus]] of the host.<ref name="Nakayama-2012">{{cite journal |vauthors=Nakayama T, Archibald JM |date=April 2012 |title=Evolving a photosynthetic organelle |journal=BMC Biology |volume=10 |issue=1 |page=35 |doi=10.1186/1741-7007-10-35 |pmc=3337241 |pmid=22531210 |doi-access=free}}</ref> Some of the cyanobacterial proteins were then synthesized by host cell and imported back into the chloroplast (formerly the cyanobacterium), allowing the host to control the chloroplast.<ref name="Nakayama-2012" /><ref name="McFadden-2001" />

Chloroplasts which can be traced back directly to a cyanobacterial ancestor (i.e. without a subsequent endosymbiotic event) are known as '''''primary plastids''''' ("[[plastid]]" in this context means almost the same thing as chloroplast<ref name="Campbell-2009c" />).<ref name="Wise-2006b" /> Chloroplasts that can be traced back to another photosynthetic eukaryotic endosymbiont are called '''''secondary plastids''''' or '''''tertiary plastids''''' (discussed below).

Whether primary chloroplasts came from a single endosymbiotic event or multiple independent engulfments across various eukaryotic lineages was long debated. It is now generally held that with one exception (the amoeboid ''Paulinella chromatophora''), chloroplasts arose from a single endosymbiotic event around two{{Nbsp}}billion years ago and these chloroplasts all share [[monophyly|a single ancestor]].<ref name="Sánchez-Baracaldo-2017" /> It has been proposed this the closest living relative of the ancestral engulfed cyanobacterium is ''[[Gloeomargarita lithophora]].''<ref>{{cite journal |vauthors=Ponce-Toledo RI, Deschamps P, López-García P, Zivanovic Y, Benzerara K, Moreira D |date=February 2017 |title=An Early-Branching Freshwater Cyanobacterium at the Origin of Plastids |journal=Current Biology |volume=27 |issue=3 |pages=386–391 |bibcode=2017CBio...27..386P |doi=10.1016/j.cub.2016.11.056 |pmc=5650054 |pmid=28132810}}</ref><ref>{{cite journal |vauthors=de Vries J, Archibald JM |date=February 2017 |title=Endosymbiosis: Did Plastids Evolve from a Freshwater Cyanobacterium? |journal=Current Biology |volume=27 |issue=3 |pages=R103–R105 |bibcode=2017CBio...27.R103D |doi=10.1016/j.cub.2016.12.006 |pmid=28171752 |doi-access=free}}</ref><ref name="López-García-2017">{{cite journal |vauthors=López-García P, Eme L, Moreira D |date=December 2017 |title=Symbiosis in eukaryotic evolution |journal=Journal of Theoretical Biology |volume=434 |pages=20–33 |bibcode=2017JThBi.434...20L |doi=10.1016/j.jtbi.2017.02.031 |pmc=5638015 |pmid=28254477}}</ref> Separately, somewhere about 90–140&nbsp;million years ago, this process happened again in the [[amoeboid]] ''[[Paulinella]]'' with a cyanobacterium in the genus ''[[Prochlorococcus]]''. This independently evolved chloroplast is often called a ''chromatophore'' instead of a chloroplast.<ref name="Macorano-2021">{{Cite journal |last1=Macorano |first1=Luis |last2=Nowack |first2=Eva C.M. |date=13 September 2021 |title=Paulinella chromatophora |url=https://linkinghub.elsevier.com/retrieve/pii/S0960982221009830 |journal=Current Biology |language=en |volume=31 |issue=17 |pages=R1024–R1026 |doi=10.1016/j.cub.2021.07.028|pmid=34520707 |bibcode=2021CBio...31R1024M }}</ref><ref group="Note" name=":0">Not to be confused with [[chromatophore]]—the pigmented cells in some animals—or [[Chromatophore (bacteria)|chromatophore]]—the membrane associated vesicle in some bacteria.</ref>

Chloroplasts are believed to have arisen after [[Mitochondrion|mitochondria]], since all [[eukaryote]]s contain mitochondria, but not all have chloroplasts.<ref name="Campbell-2009c" /><ref>{{cite journal |vauthors=Archibald JM |date=January 2009 |title=The puzzle of plastid evolution |journal=Current Biology |volume=19 |issue=2 |pages=R81-8 |bibcode=2009CBio...19..R81A |doi=10.1016/j.cub.2008.11.067 |pmid=19174147 |s2cid=51989 |doi-access=free}}</ref> This is called ''[[serial endosymbiosis]]''—where an early eukaryote engulfed the [[mitochondrion]] ancestor, and then descendants of it then engulfed the chloroplast ancestor, creating a cell with both chloroplasts and mitochondria.<ref name="Campbell-2009c" />